Cell design for a trawl system and methods

ABSTRACT

Mesh bars ( 35, 283 ) of a trawl ( 13, 263 ) include at least a portion having a corkscrew-shaped pitch which exhibits a hydrofoil-like effect. Such mesh bars ( 35, 283 ) are preferably formed from a material having a substantially incompressible cross-sectional shape. By appropriately selecting the lay and leading edge of mesh bars ( 35, 283 ), movement of the trawl ( 13, 263 ) through the water entrained environment creates a pressure differential and lift across that portion of mesh bars ( 25, 283 ) which exhibit the hydrofoil-like effect. The lift thus created increases performance characteristics of the trawl ( 13, 263 ) including increased trawl volume, improved trawl shape, and reduced vibration, noise, and drag. Obtaining the greatest improvement of trawls ( 13, 263 ) requires controlling a pitch range for twisted product strands (e.g. twisted ropes) ( 36, 37 ), and for straps ( 284 ) forming mesh bars ( 35, 283 ). For straps ( 284 ), control of a width to thickness ratio also significantly affects performance of the trawl ( 13, 263 ).

This is a United States national stage application of prior copendingInternational Application No. PCT/US98/07848, filed Apr. 14, 1998, whichin turn is a continuation-in-part of prior copending ProvisionalApplication No. 60/043,618, filed Apr. 14, 1997, the benefit of thefiling dates of which are hereby claimed under 35 U.S.C. §120.

TECHNICAL FIELD

The present invention relates to an improved mesh cell design for atrawl system (that by definition is iterated or cloned in varyinggeometric patterns) providing improved shaping and performance,especially when incorporated in mid-water or bottom trawls of suchsystems.

BACKGROUND ART

It is well understood that the basic cell of a selected portion of everytrawl system is the unit cell (called mesh cell hereinafter). Theselected portions of the trawl system is then built by repeating theshape of the basic mesh cell.

It is axiomatic that the ability to predict the overall shape andperformance of the finished product depends entirely on the shape andstructural integrity of that single basic mesh cell. Heretofore, propertrawl making was a two-step process that involved initial constructionof undersized mesh cells, and setting the knots and mesh sizes by thesubsteps of depth stretching and heat setting involving turning thefinished mesh in direction opposite to its natural bent and applyingfirst pressure, and then heat to set the knots.

Materials used in mesh cell construction can be plastics such as nylonand polyethylene but other types of natural occurring fibers also can be(and have been) used. Single, double (or more) strands make up a threador twine composed of, say, nylon, polyethylene and/or cotton.Additionally, in making the mesh portion of conventional trawlsparticularly mid-water trawls especially the forward section meshportion thereof, braided cords and twisted ropes of natural andsynthetic materials, bonded and unbonded, and cables have been used.However, the pitch of any braided or twisted thread, such as a twine,cord and/or rope (distance between corresponding points along one of thestrands constituting one turn thereof which is analogous to the pitchbetween corresponding screw threads) either has usually been small, orhas produced shallow or narrow depressions. Conventional trawl makingpractices balance the towing force generatable by a vessel against thelargest possible trawl for a particular fishing condition, i.e. a trawlhaving the minimum possible drag. Thus, conventional trawl makers aretaught to use the smallest possible diameter twine to reduce drag.Accordingly, meshes in conventional trawls, and especially the mesh ofthe forward sections of mid-water trawls, have been made of twines,including conventional three strand twisted twines of any pitchincluding loose pitch, that have relatively shallow or narrow anduniform spiral depressions, or smaller diameter braided twines having anequivalent breaking strength. Moreover, modern manufacturing processesusing threads, such as twines, cords, cables or ropes to form meshcells, have always been designed to produce mesh cells in which twistdirection of the individual bars comprising each mesh cell, if any, isalways the same. None have proposed the systematic and regular use ofdifferently oriented twist for individual mesh bars of the mesh cell inthe manner of the present invention.

Even though various Japanese Patent Applications superficially describemesh cells for nets in which mesh bars have differing lay directions,(see for example, Jap. Pat. Apps. 57-13660, 60-39782 and 61-386), themesh bars employ conventional, essentially smooth twine or rope. Thepatent applications disclose differing lay directions of conventional,essentially smooth twine or rope for balancing residual torque withinthe net structure during its deployment and use, not for generating liftthat enhances of trawl system performance. The first-mentionApplication, for example, states that its purpose is to provide “netlegs with different twist directions according to a fixed regularpattern so that torsion and torque of said net legs are mutuallycanceled.” The use of conventional, essentially smooth twine or ropewill not yield substantial lift any different from conventional nets.

As set forth in published Patent Cooperation Treaty (“PCT”)International Patent Application, International Publication Number WO97/13407, International Publication Date Apr. 17 1997, (“the PCT patentapplication”) it has been recently discovered that threads, such astwines, cords, braided cords, cables, ropes or straps, may beadvantageously twisted, during assembly of trawl net meshes into aloose, corkscrew-shaped pitch establishing helical grooves that aredeeper and/or broader than the depressions in conventional tightly orloosely twisted multi-strand ropes or cables making up conventional meshbars. During field operations in a water entrained environment, properlyorienting mesh bars having the loose, corkscrew-shaped pitch produceslift that increases a performance characteristic of a trawl system suchas increased trawl volume (particularly in shallow water) in comparisonwith a trawl made from conventional mesh, improved trawl shape, andreduced vibration, noise, and drag. Trawl performance improves eventhough, contrary to conventional trawl design, mesh bars having theloose, corkscrew-shaped pitch have a diameter (or shadow area) largerthan corresponding mesh bars of a conventional trawl.

DISCLOSURE OF INVENTION

An object of the present invention is to provide further improved trawlsystems.

Yet another object of the present invention is to provide trawl systemshaving improved performance characteristics.

Briefly, the present invention improves upon the basic discoverydisclosed in the PCT patent application that individual bars of a meshcell can be formed to act as mini-hydrofoils in field operations. Duringfield operations in a water entrained environment, the trawl disclosedin the PCT patent application becomes disposed symmetrically about acentral axis. The disclosed trawl includes a plurality of mesh cells,each mesh cell having at least three mesh bars. Each mesh bar in thetrawl intersects with at least one other mesh bar. During fieldoperations with the trawl in a water entrained environment, at least aportion of at least one of the mesh bars of at least one of the meshcells in the trawl exhibits a substantial hydrofoil-like effect thataids in increasing a performance characteristic of a trawl system. Thatportion of mesh bars in accordance with the present invention whichgenerate substantial hydrodynamic lift is preferably formed from amaterial that has a substantially incompressible cross-sectional shape,is offset from the central axis of the trawl, and is formed with ahydrofoil shape that:

1. has a lay with a loose, corkscrew-shaped pitch establishing acorkscrewing groove that provides cambered sections; and

2. is oriented to establish leading and trailing edges for that portionof mesh bars which generate hydrodynamic lift.

The lay of that portion of mesh bars which generate hydrodynamic lifthas an orientation relative to a receding direction, and the leadingedge for that portion of mesh bars which generate hydrodynamic lift,when normalized to the receding direction relative to the central axis,resides at a side of the mesh bar. Pairs of lay and the leading edge areselected for mesh bars from a group consisting of:

1. a left-hand lay, and the leading edge being a right side of the meshbar as viewed in the receding direction; and

2. a right-hand lay, and the leading edge being a left side of the meshbar as viewed in the receding direction.

If the lay and leading edge are selected from the preceding group, thenmovement of the mesh bar in accordance with the present inventionthrough the water entrained environment relative to a water flow vectorthat is neither parallel nor perpendicular to the mesh bar creates apressure differential across that portion of mesh bars which generatehydrodynamic lift. The pressure differential thus created across suchmesh bars establishes a lift vector relative to the central axis of thetrawl, most commonly directed away from the central axis of the trawl.Consequently, the lift vector created by movement of the mesh bars whichhave a portion that generate hydrodynamic lift increases the performancecharacteristic of the trawl which is selected from a group consisting ofsubstantially increased trawl volume (particularly in shallow water) incomparison with a trawl made from conventional mesh, improved trawlshape, and reduced vibration, noise, and drag.

Various other aspects of the present invention further improve theperformance of trawl systems. Thus, properly controlling the shape,arrangement, and distribution of strands assembled to form a mesh barfurther improves a trawl in accordance with the present invention. Theproper pitch for the loose, corkscrew-shape is advantageously controlledso the pitch of each mesh bar is in a range of 3 d to 70 d, with a rangeof 5 d to 55 d being preferred, where d is:

1. for a pair of twisted strands forming a mesh bar, the diameter of thesmaller strand of the pair;

2. for mesh bars that include more than a pair of twisted strands orstrands of differing diameters, the diameter of the next-to-largestdiameter twisted strand; or

3. for straps forming a mesh bar, the width of the strap.

Within the preferred pitch range, a pitch of 5 d to 15 d generallyproduces maximum lift for mesh bars formed from product strands, while apitch of 25 d to 55 d generally produces minimum drag for mesh barsformed from product strands.

For mesh bars formed by straps, a pitch of 8 d to 30 d generallyproduces maximum lift, while a pitch of 9 d to 21 d generally producesminimum drag. A ratio for the width of the strap to a thickness of thestrap is preferably in a range of 1.5:1 to 20:1. Straps for which theratio is in a range from 2.5:1 to 2.75:1 provide both low drag and goodlift. Straps for which the ratio is in a range from 2.75:1 to 10.0:1provide high lift. Straps for which the ratio is in a range from 1.8:1to 2.5:1 provide low drag with good lift. Straps for which the ratio isin a range from 1.5:1 to 1.8:1 exhibit lower drag. Straps in the rangefrom 1.8:1 to 2.5:1 may be used advantageously in the mid-section and/orback-end of the trawl. Conversely, straps in the range from 2.75:1 to10.0:1 may be used advantageously in the front-end, particularly near aleading edge of the trawl.

These and other features, objects and advantages will be understood orapparent to those of ordinary skill in the art from the followingdetailed description of the preferred embodiment as illustrated in thevarious drawing figures.

DEFINITIONS

MESH is one of the openings between threads, ropes or cords of a net.

MESH CELL means the sides of a mesh and includes at least three sidesand associated knots or equivalent couplers oriented in space. Aquadratic mesh cell has four sides with four knots or couplers, and isusually arranged to form a parallelogram (including rectangular andsquare), with diamond-shaped mesh (trawl mesh) being preferred. Atriangular mesh cell has three sides and three knots or couplers. Ahexagonal mesh cell has six sides and six knots or couplers.

MESH BARS means the sides of a mesh cell.

CELL means a trawl construction unit, fishing net or the like andincludes both a mesh cell relating to enclosable sides of the mesh ofthe trawl or net itself, as well as to upper bridle and frontropes usedin towing the trawl or net through a water column to gather marine life.

CELL BAR means both the sides of a mesh cell and the elements that makeup the upper bridle, frontropes and tow lines.

RIGHT- AND/OR LEFT-HANDEDNESS IN A RECEDING DIRECTION along a cell barinvolves establishing a central axis for the trawl, net or the like towhich the mesh cell associated with the cell bar belongs. Then anormalized imaginary giant stick figure, that is depicted in FIGs. ofthe PCT patent application, is positioned so his feet intersect thecentral axis, are rotatable about the central axis, his body penetratesthrough the cell bar, and his back is positioned perpendicular to andfirst intersects the water flow vector for the moving trawl, net or thelike. The right- and/or left-handedness of the cell bar is thendetermined using the location of either his right or his left armirrespective of the fact that the position of the cell bar is offsetfrom the central axis.

THREADS are composed of synthetic or natural fibers. Firstly, for thepresent invention a thread can comprise two strands twisted along thelongitudinal axis of symmetry in a loose fashion with a pitch in a rangeof 3 d-70 d, where d is:

1. for a pair of twisted strands forming a mesh bar, the diameter of thesmaller strand of the pair; or

2. for mesh bars that include more than a pair of twisted strands orstrands of differing diameters, the diameter of the next-to-largestdiameter twisted strand. Or secondly, for the present invention a threadcan comprise a extruded, woven, braided, or plaited strap that istwisted along its longitudinal axis of symmetry in a loose fashion witha pitch in a range of 3 d-70 d, where d is the width of the strap.

STRAP is a flexible element of synthetic or natural fibers that forms amesh bar, the strap having a cross-section that is generally rectangularor can be quasi-rectangular with rounded short sides and elongated longsides with or without camber. In operation, the strap acts as ahydrofoil, preferably twisted along its longitudinal axis, wherein theshort sides form interchanging leading and trailing edges.

PRODUCT STRAND includes the synthetic or natural fibers or filamentsused to form the construction unit of the invention which is preferably,but not necessarily, the product of a conventional manufacturingprocess, usually made of nylon, polyethylene, cotton or the like twistedin common lay direction. Such strand can be twisted, plaited, braided orlaid parallel to form a sub-unit for further twisting or other usewithin a mesh bar or a cell bar in accordance with the invention.

NET is a meshed arrangement of threads that have been woven or knottedor otherwise coupled together usually at regular intervals or atintervals that vary usually uniformly along the length of the trawl.

TRAWL is a large net generally in the shape of a truncated cone trailedthrough a water column or dragged along a sea bottom to gather marinelife including fish.

CODEND is a portion of a trawl positioned at the trailing end thereofand comprises a closed sac-like terminus in which the gathered marinelife including fish are trapped.

FRAME is a portion of the larger sized meshes of a net or trawl uponwhich is overlaid (and attached by a binding) a netting of conventionaltwist.

PANEL is one of the sections of a trawl and is made to fit generallywithin and about frames shaped by riblines offset from the longitudinalaxis of symmetry of the trawl.

PITCH is the amount of advance in one turn of one product strand twistedabout another product strand (or strands) when viewed axially, or commonadvance of the twist of a strap along its axis of symmetry. For productstrands, pitch values are determined with respect to the diameter of thenext-to-largest product strand. For straps, pitch values are determinedwith respect to the width of the strap.

LAY is the direction in which the strands or the strap wind when viewedaxially and in a receding direction.

INTERNAL LAY OR TWIST is the direction in which synthetic or naturalfibers comprising each product strand are wound when such strand isviewed axially and in a receding direction.

INTERNAL BRAID describes the method of formation of a particular productstrand.

FRONTROPE(S) is a term that includes all lines located at perimeter edgeof the mouth of the trawl, net or the like, such as headrope, footrope(or bottomrope) and breast lines. The frontropes have a number ofconnections relative to each other and to the bridle lines.

BRIDLES relates to lines that intersect the frontropes and attach to thetow lines. For a particular port or starboard tow line, a pair ofbridles extend from a common connection point therewith, back to thefrontropes.

TRAWL SYSTEM is a term that includes the trawl, net or the like inassociation with the tow lines therefor as well as the bridles lines.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a illustrative side view of a trawl system depicting amid-water trawl being towed by a vessel;

FIG. 2 is a detail top view of the trawl of FIG.1;

FIG. 3 is a fragmentary enlargement of a mesh cell included in the trawldepicted in FIGS. 1 and 2;

FIG. 4 is a cross-section taken along line 4—4 of FIG. 3 illustratingone possible configuration for product strands that form mesh bars ofthe mesh cell;

FIGS. 5, 6 and 7 are sections akin to that depicted in FIG. 4illustrating various alternative configurations of product strands;

FIG. 8 is a side view of an alternate trawl system including a mid-watertrawl being towed by a vessel;

FIG. 9 is a detail top view of the trawl of FIG. 8;

FIG. 10 is another fragmentary enlargement of a mesh cell included inthe trawl depicted in FIGS. 8 and 9;

FIG. 11 a cross-section taken along line 11—11 of FIG. 10 illustratingone possible configuration for straps that form mesh bars of the meshcell;

FIGS. 12-19 are sections akin to that depicted in FIG. 11 illustratingvarious alternative configurations for straps;

FIG. 20 is a partially-sectioned elevational view of a strap having aparallelogram cross-sectional shape together with a shackle adapted foruse with the parallelogram-shaped strap;

FIGS. 20a and 20 b are cross-sectional elevational views ofalternatively shaped, parallelogram cross-sectional straps similar tothat depicted in FIG. 20;

FIG. 21 is a plan view illustrating coupling together four shackles ofthe type depicted in FIG. 20 to form an X-pattern that is used inassembling parallelogram shaped straps into a mesh cell of a trawl;

FIGS. 22 and 23 are plan views illustrating fabrication of smaller sizedmesh cells using straps;

FIGS. 23a-23 e are cross-sectional views of alternative embodimentstraps having “S” or “Z” cross-sectional shapes;

FIGS. 24a is an elevational cross-sectional view, orthogonal to alongitudinal axis of a woven strap, depicting various fibers that makeup the strap;

FIG. 24b is an elevational cross-sectional view along the longitudinalaxis of the woven strap taken along the line 24 b-24 b in FIG. 23ahaving a structure that may be modified to provide a cross-sectionalshape similar to those depicted in FIGS. 23a-23 e;

FIG. 25 is a plan view illustrating fabrication of smaller sized meshcells using straps using an alternative method to that illustrated inFIGS. 22 and 23;

FIGS. 26a and 26 b depict cross-sectional shapes for alternativestructure straps having angled shaping strips disposed along leading andtrailing edges of the straps;

FIGS. 27a and 27 b are plan views illustrating shapes for alternativestructure straps having angled shaping strips disposed along leading andtrailing edges of the straps;

FIGS. 28a through 28 c are plan views illustrating various differentconfigurations for corkscrew-shaped product strands; and

FIG. 29 is a plan view of a mesh bar in which one product strand spiralsaround another product strand.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, a towing vessel 10 at a surface 11 of a body ofwater 12, tows a mid-water trawl 13 of a trawl system 9. The trawl 13 ispositioned between the surface 11 and an ocean bottom 14. The trawl 13can be connected to the towing vessel 10 in many ways, such as by a maintowing line 18 connected through door means 19, towing bridles 20 andmini-bridles 21, 22. A series of weights 23 is attached to mini-bridle22. Likewise, the shape and pattern of the trawl 13 can vary as is wellknown in the art. As shown, the trawl 13 has a forward section 24 thatincludes forward projecting wings 25 for better herding at mouth 26. Theforward section 24, including wings 25, is seen to define a mesh sizethat is larger than that used for a mid-section 27, back-end 28, orcodend 29 of the trawl 13.

FIG. 2 illustrates the wing 25 of the trawl 13 of FIG. 1 in more detailand includes a series of mesh cells 30 of quadratic cross-section thatare part of panel 31 and are offset from axis of symmetry 32 of thetrawl 13. The size of mesh cells 30 is determined by a distance betweenadjacent knots or equivalent couplers 34. Different sections of thetrawl 13, and even different regions within a section, use differentsize mesh cells 30, which generally form a repeating pattern within thatsection or region of a section.

As shown in FIG. 3, the mesh cells 30 each have a longitudinal axis ofsymmetry 30 a, and are formed of a series of mesh bars 35 that includeseveral product strands 36, 37. As explained in greater detail below,the product strands 36, 37 may be twisted about a common axis ofsymmetry 38 in either one of two lay directions: clockwise orcounterclockwise as viewed axially along common axis of symmetry 38 andin a receding direction established upstream of the trawl 13. Formingthe cork-screw shape of the mesh bars 35 is described in the PCT patentapplication, that is hereby incorporated by reference.

As indicated in FIGS. 1 and 2, the length of mesh bars 35 varies alongthe length of the trawl 13. For example, the mesh bars 35 in the forwardsection 24 have a length of at least 10 ft (304.8 cm). Alternatively,the mesh bars 35 in the mid-section 27 of the trawl 13 have lengthbetween 10 ft. (304.8 cm) and 0.75 ft (22.86 cm). The mesh bars 35 ofthe back-end 28 have a length less than 0.75 ft (22.86 cm).

FIG. 4 shows one configuration for the product strands 36, 37 in greaterdetail. As shown, the product strands 36, 37 vary in diameter whereinprincipal product strands 36 a, 36 b are of a larger, equal diameterthan auxiliary product strands 37 located in recesses 40 formed betweenthe principal product strands 36 a, 36 b. Such auxiliary product strands37 each consists of a product strand 37 a of smaller diameter thanproduct strands 36 a, 36 b sandwiched between a pair of even smallerdiameter auxiliary product strands 37 b. The larger product strands 36a, 36 b have outer surfaces 39 in tangential contact with each otheralong a single, three dimensional contact curve. The product strands 37tangentially contact the outer surfaces 39 of the larger product strands36 a, 36 b at locations offset from that of the latter. Theconfiguration depicted in FIG. 4 produces a hydrofoil section havingsurprisingly superior results in operations.

FIGS. 5, 6 and 7 show variations of the invention akin to that depictedin FIG. 4.

FIG. 5 illustrates a variation on the number and shape of the productstrands 36, 37. That is, a single larger product strand 36 a′ can bemounted in tangential contact with smaller strand 37 a′ with a stillsmaller strand 37 b′ located in recesses 40′ therebetween.

FIG. 6 illustrates another variation from the configuration depicted inFIG. 5 which adds additional auxiliary product strands 46 of evensmaller diameter than those of unequal diameter principal andintermediate product stands 36 a″, 37 a″ at tangential positions withinrecesses 40″. That is, such product strands 46 are located in the tworecesses 40″ formed adjacent to a single tangential contact point 47between the product stands 36 a″, 37 a″.

As shown in FIG. 7, the number, orientation and size of product strands,generally indicated at 50 has changed. Two smaller product strands 50 a,50 b of equal diameter sandwich a larger diameter product strand 50 c.The product strands 50 a, 50 b and 50 c establish recesses 51 whichreceive a plurality of much smaller diameter product strands 52. Thecross-sectional shape depicted in FIG. 7, even though formed fromproduct strands, approaches that of a strap that will be discussed ingreater detail herein below. As a cross-sectional shape of combinedproduct strands approaches that of a strap, parameters for straps,rather than for product strands, should be used in designing the trawl.

It should be pointed out that product strands are synthetic or naturalfibers or filaments which are preferably but not necessarily the productof a conventional manufacturing process, usually made of nylon,polyethylene, cotton or the like twisted in common lay direction. Suchstrand can be twisted, plaited, braided or laid parallel to form asub-unit for further twisting or other use within mesh bars 35 inaccordance with the teachings of the present invention and the PCTpatent application. In general, bonded product strands exhibitsignificantly greater hydrodynamic lift, e.g. a 1.3 to 1.7 or greaterincrease in lift, than unbonded product strands of identical diameter.To minimize drag while maximizing hydrodynamic lift a densely laid, heatset and bonded product strand, densely braided product strand, or strap,each of which has a substantially incompressible cross-sectional shapeand a somewhat roughened surface, is preferred for preserving, duringand after assembly of the trawl 13 or 283, the profile and configurationof the mesh bars 35 and 283, as well as that of the cambered sectionscreated by the loose, corkscrew-shape, particularly upon application oftensile forces to mesh bars 35 and 283. Alternatively, in applicationswhere maximizing hydrodynamic lift is a primary consideration andbreaking strength and drag requirements are easily satisfied, bondingmay be used to make product strands or straps substantiallyincompressible while reducing manufacturing cost. Bonding resists atendency for product strands or straps to compress during assembly andfield operations, and therefore better preserves designed hydrofoilcharacteristics of the mesh bars 35 and 283. Variations in applying abonding material during assembly of mesh bars 35 further permitscontrolling their external shape and filling gaps between productstrands. A urethane polymeric material, or material having similarproperties, is adequate as a bonding material.

FIG. 8 shows towing vessel 260 at a surface 261 of a body of water 262towing a mid-water trawl 263 of a trawl system 264. The trawl 263 ispositioned between the surface 261 and a bottom 265, and connected tothe towing vessel 260 via main tow lines 268, door means 269, towingbridles 270, mini bridles 270 a, and frontropes 271 that includebreastlines 271 a, and headropes 271 b. A series of weights 272 attachto the towing bridles 270. The trawl 263 is made up of four panels(sides, top and bottom panels), and includes wings 274 for betterherding at mouth 275. As shown in FIG. 9, the forward section includes aseries of mesh cells 280 of parallelogram design that are offset from acentral axis of symmetry 281.

FIG. 10 show the mesh cells 280 in more detail. As shown in FIG. 10, themesh cells 280 each have an axis of symmetry 282 that is offset from thecentral axis of symmetry 281 of the trawl 263. Since the shape of thetrawl 263 varies along the axis of symmetry 281 from almostcylindrically shaped at the wings 274 to a more frustoconical shape overthe remainder, the orientation of the axes of symmetry 282 of individualmesh cells 280 vary with respect to the axis of symmetry 281 of thetrawl 263. Thus, with respect to the axis of symmetry 281 of the trawl263, the axis of symmetry 282 of the mesh cells 280 may be parallel,non-parallel and non-intersecting, and/or non-parallel and intersecting.But note that axes of symmetry 282 of the mesh cells 280 are alwaysoffset from the axis of symmetry 281 of the trawl 263. In theillustration of FIG. 10, the mesh bars 283 of each mesh cell 280 arerespectively formed by straps 284 arranged in a X-pattern using a seriesof mechanical connections 285 to maintain such orientation. Each strap284 is twisted, such direction being normalized to the recedingdirection of use, as indicated by arrow 286. Such twisting of the straps284, either left-handed or right-handed as required, occurs about anaxis of symmetry 288 of the strap 284 in accordance with the teachingsset forth in the PCT patent application. As a result, leading andtrailing edges 287 are formed.

FIG. 11 illustrates one possible cross-sectional configuration for thestrap 284. The configuration depicted in FIG. 11 is basically aparallelogram with diametrically opposite corners 84 a being truncatedwhile diametrically opposite corners 284 b have pointed edges. Sides 284c are approximately of equal length. The loose, corkscrew-shaped pitchis directly related to the length between opposite corners 284 a, i.ethe width of the strap 284. Generally, for generating hydrodynamic liftand reducing drag a densely constructed strap 284, formed from a denselywoven and bonded strap material, having a substantially incompressiblecross-sectional shape and a somewhat roughened surface is preferred.Variations in applying a bonding material permits controlling theexternal shape of a strap. A urethane polymeric material, or materialhaving similar properties, is adequate as a bonding material.

FIGS. 12-19 show variations of the invention akin to that depicted inFIG. 11.

In the illustration of FIG. 12, corners 300 of strap 284′ are pointedrather than being truncated as depicted in FIG. 11. Opposite corners 301define angles α and β where β>α. Sides 302 are approximately of equallength so the cross-section is that of an equilateral parallelogram. Theloose, corkscrew-shaped pitch is directly related to the lengths betweenfar corners 300.

FIG.13 depicts a hexagonal cross-section for strap 284″ having sides 305of approximately the equal length. Corners 306 define an included angleγ while corners 307 define included angles δ where δ>γ. The loose,corkscrew-shaped pitch is directly related to the length between thecorners 306.

In FIG. 14, strap 284″′ is formed of a quasi-rectangular cross-sectionby the inclusion of a single larger diameter product strand 400sandwiched between a pair of smaller diameter product strands 401, thatare all enclosed within a sheath 402. The smaller diameter productstrands 401 make tangential contact with the product strand 400 atcontact points 403 lying in a plane that intersects axes of symmetry ofthe product strands 400, 401.

In FIG. 15, strap 284″″ is of a quasi-rectangular cross-section formedof a strand 410 encircled with a larger sheath 411 which is gathered atdiametrically opposite locations to form oppositely positioned ridges413.

In FIG. 16, the strap 284″″′ is formed of a pair of larger diameterstrands 415, intermediate diameter strands 416 located within recesses417 of the larger strands 415, and a series of smaller diameter strands418, all surrounded by a sheath 420.

In FIG.17, strap 284″″″ is triangular in cross-section including sides425 and hypotenuse 426 opposite of right angle Since the side 425 a islonger than side 425 b, the cross-section is termed “asymmetric”.

In FIG.18, strap 284″″″′ is quasi-triangular in cross-section includingsides 428 and hypotenuse 429 opposite of right angle γ. Since the side428 a is longer than side 428 b and the fact that the side 428 b andhypotenuse 429 are curved (meeting at corner 430), the cross-section istermed “quasi-asymmetric”.

In FIG.19, strap 284″″″″ is again quasi-triangular in cross-sectionincluding sides 430 and hypotenuse 431 opposite of right angle ζ. Sincethe side 430 a is longer than side 430 b and the fact that the side 430b and hypotenuse 431 are curved (and do not meet at any identifiablelocation), the cross-section is termed “quasi-asymmetric”.

FIGS. 23a through 23 c depict various “S” or “Z” cross-sectional shapesthat provide improved performance when used for the straps 284 of meshcells 280. As depicted in FIGS. 23a-23 e, the “S” or “Z” cross-sectionalshapes for the straps 284 add a drooping leading edge 338 and a raisedtrailing edge 339 to the rectangular cross-sectional shape of aconventional strap. During testing, twisted straps 284 having across-sectional shape such as those illustrated in FIGS. 23a-23 e haveexhibited greater hydrodynamic lift and lower drag than a simple,rectangularly-shaped strap 284.

FIG. 24a illustrates various fibers that are assembled to form a simple,rectangularly-shaped strap 284. In the illustration of FIG. 24a, spacesbetween various fibers making up the strap 284 are greatly exaggeratedto facilitate illustration of the structure of the strap 284. The fibersof the strap 284 include larger-diameter, longitudinal core fibers 342which extend along the length of the strap 284. Smaller-diameterlongitudinal fibers 344, arranged on both sides of the core fibers 342,also extend along the length of the strap 284. Lateral fibers 346encircle and bind together the core fibers 342 and longitudinal fibers344. Surface fibers 348 are woven about he lateral fibers 346independently on each side of the core fibers 342 and the longitudinalfibers 344. Finally, binder fibers 352 completely encircle the lateralfibers 346 located on both sides of the core fibers 342 and longitudinalfibers 344 thereby securing together the lateral fibers 346, the corefibers 342 and longitudinal fibers 344.

FIG. 24b depicts a cross-section of the strap illustrated in FIG. 24a inwhich two of the smaller-diameter longitudinal fibers 344 located alongdiametrically opposite edges of the strap 284 have been replaced withlarger diameter fibers 354. Modifying the structure of a conventionalstrap 284 by including two such larger diameter fibers 354 asillustrated in FIG. 24b results in a strap 284 having a cross-sectionalshape similar to those illustrated in FIGS. 23a-23 e. Appropriatelyselecting a diameter for the larger diameter fibers 354 permitsadjusting the respective extensions of the leading edge 338 and thetrailing edge 339.

FIG. 20 illustrates a strap 284 having a cross-sectional shape that issubstantially that of a parallelogram, i.e. similar to the shape of thestrap 284′ depicted in FIG. 12. The parallelogram-shaped strap 284depicted in FIG. 20 is assembled by appropriately arranging and thenlaminating together a stack of individual, rectangularly shaped straps304. In general, the straps 304 may be secured to each other in variousways such as by sewing, clamping, riveting, gluing or an equivalenttechnique. However, for straps 304 made from polymeric materialslamination appears to be preferably effected by ultrasonic bonding orwelding.

Also depicted in FIG. 20 is a shackle 312 that is particularly adaptedfor use with the strap 284 depicted there. The shackle 312 includes asurface 314 that slopes with respect to a longitudinal axis of the strap284 extending to the right of the shackle 312. The sloping surface 314contacts one surface of the parallelogram-shaped strap 284 while avertical surface 316 of the shackle 312, that is oriented perpendicularto the longitudinal axis of the strap 284 extending to the right of theshackle 312, contacts an adjoining surface of the strap 284. The slopingsurface 314 in combination with the vertical surface 316 of the shackle312 prevent the strap 284 from twisting with respect to the shackle 312upon application of a tensile stress to the strap 284.

FIG. 21 depicts four shackles 312 of the type depicted in FIG. 20through each of which pass straps 284 having the shape depicted in FIG.20. The four shackles 312 are flexibly joined together andinterconnected by a length of spliced rope 322 to form the X-pattern oflarger mesh cells 280 of the trawl 13 depicted in FIGS. 8 and 9, e.g.the mesh cells 280 that form the forward section including wings 274 anda mid-section 276 thereof. In this way the shackles 312 and the splicedrope 322 mechanically join together the straps 284.

FIGS. 20a and 20 b depict alternative embodiments of theparallelogram-shaped strap 284 depicted in FIG. 20. As with the strap284 depicted in FIG. 20, the straps 284 depicted in FIGS. 20a and 20 bare respectively assembled by laminating together two (2) and four (4)individual, rectangularly shaped straps 304. Even in the absence oftwisting, parallelogram-shaped straps 284 such as those depicted inFIGS. 20, 20 a and 20 b create a hydrodynamic lifting force that isapproximately one-half of the lifting force for the same strap whentwisted. The direction of the hydrodynamic lifting force, i.e.horizontally to the left or right in FIGS. 20a and 20 b, depends uponthe relationship between the laminated straps 304 and the direction ofwater flow.

In addition to using twisted straps for the mesh cells 280 that form thewings 274 and mid-section 276 of the trawl 263, it is also advantageousto use such twisted straps for an back-end 277 and for a codend 278 ofthe trawl 263. However, since much smaller mesh cells 280 are requiredfor the back-end 277 and for the codend 278 than for the wings 274 andmid-section 276, it is economically impractical to assemble small meshcells 280, e.g. 4 inch mesh cells 280, in the way illustrated in FIG.21. Instead, as illustrated in FIGS. 22 and 23, smaller mesh cells 280may be fabricated by arranging elongated straps 332, preferably madefrom a polymeric material and twisted as described above, along zigzagrows of pins 334 included in a jig. The arrangement of the twistedstraps 332 about the pins 334 juxtaposes short sections 336 of twoadjacent straps 332 between immediately adjacent pairs of pins 334. Thesmaller mesh cells 280 are then established by laminating together theshort sections 336, preferably by ultrasonic bonding or welding, or anyof the other methods described above. Laminated ultrasonic bonding orwelding of the short sections 336 appears to be preferred formaintaining the strength of the strap 332, and to avoid distorting theshape of the twisted straps 332 between successive short sections 336along each strap 332.

A jig for fabricating the smaller mesh cells 280 may orient the pins 334either in a horizontal or in a vertical plane. If the jig orients thepins 334 in a horizontal plane, then the straps 332 to be laminatedtogether are arranged between pairs of pins 334 that are located alongone edge of the jig while fabricated mesh cells 280 are stored on anopposite side of the jig during assembly and fabrication of immediatelysubsequent rows of mesh cells 280. If the jig orients the pins 334 in avertical plane, then the straps 332 to be laminated together arearranged between pairs of pins 334 that are located along an upperportion of the jig while fabricated mesh cells 280 are stored in a lowerportion of the jig or on a floor of a fabrication area during assemblyand fabrication of immediately subsequent rows of mesh cells 280.

The vertically oriented apparatus for forming the smaller mesh cells 280from appropriately twisted straps 332 may be adapted for machinearrangement of the straps 332 and machine lamination of the shortsections 336. Such a mechanical apparatus for fabricating the mesh cells280 need employ only two row of pins 334 arranged in the zigzag manner,and then add only two more twisted straps 332 which form two more rowsof mesh cells 280 to those mesh cells 280 previously fabricated usingthe same two zigzag rows of pins 334. Even faster vertically orientedmachine fabrication of smaller mesh cells 280 may be effected byestablishing a linear array of straps 332 along an upper portion of amachine. All of the straps 332 then feed downward concurrently in azigzag manner guided by pins that oscillate horizontally back and forthwithin a single cell in synchronism with the descending straps 332. Inthis way, the short sections 336 of a particular strap 332 would firstbe juxtaposed with a short section 336 of a strap located on one side ofthe particular strap 332, and then subsequently be juxtaposed with ashort section 336 of a strap located on the opposite side of theparticular strap 332.

Instead, as illustrated in FIGS. 22 and 23, smaller mesh cells 280 maybe fabricated by arranging elongated straps 332, preferably made from apolymeric material and twisted as described above, along zigzag rows ofpins 334 included in a jig. The arrangement of the twisted straps 332about the pins 334 juxtaposes short sections 336 of two adjacent straps332 between immediately adjacent pairs of pins 334. The smaller meshcells 280 are then fixed by laminating together the short sections 336,preferably by ultrasonic bonding or welding, or any of the other methodsdescribed above. Laminated ultrasonic bonding or welding of the shortsections 336 appears to be preferred for maintaining the strength of thestrap 332, and to avoid distorting the shape of the twisted straps 332between successive short sections 336 along each strap 332.

In the method illustrated in FIGS. 22 and 23, the straps 332 twist inopposite directions on opposite sides of the pins 334. FIG. 25illustrates an alternative method for assembling smaller mesh cells 280for the trawl 263 in which straps 332 extend straight along a line thatslopes upward from left to right (indicated by broader lines), ordownward from left to right, indicated by narrower lines). Straps 332that extend in such straight lines have only a single, uniform directionof twist along their entire length, rather than an alternating directionof twist which changes at each of the pins 334 s in FIGS. 23 and 24.Similar to the assembly method described for FIGS. 23 and 24, the methodof depicted in FIG. 25 juxtaposes short sections 336 of two adjacentstraps 332. Correspondingly, the smaller mesh cells 280 are then fixedby laminating together the short sections 336 in the manner describedabove.

FIGS. 26a and 27 a illustrate straps 284 having symmetrical, angledshaping strips 372 disposed along both a first edge 374 and a secondedge 376 of straps 284. As is apparent from the illustrations, theshaping strips 372 alternately project from one side surface 382 andthen an opposite side surface 384 of the strap 284. Moreover, theshaping strips 372 wrap around either he first edge 374 or the secondedge 376 in passing from one surface 382 to the other surface 384.Properly orienting and positioning the shaping strips 372 projectingfrom one surface 382 or 384 of the strap 284 with respect to twisting ofthe straps 284 aligns that portion of the shaping strip 372 on thecambered section substantially parallel to water flow past the mesh bar283 while the portion of the shaping strip 372 on the other side 384 or382, which extends between a pair of immediately adjacent camberedsections, is oriented substantially perpendicular to water flow. Thestraps 284 that include the shaping strip 372 exhibit greaterhydrodynamic lift, improved hydrodynamic characteristics under largertwisting pitches, and increased twisting stability. The shaping strips372 may be formed in various ways such as by stitching. FIGS. 26b and 27b illustrate straps 284 for which shaping strips 372 disposed along thefirst edge 374 are formed with a different angle from the shaping strips372 disposed along the second edge 376 of straps 284.

FIGS. 28a through 28 c depict various different configurations for meshbars 35 having the loose, corkscrew-shaped pitch that establishes deepgrooves 391 formed by the corkscrewing of the product strands 36, 37. Inthe illustration of FIG. 28a, the product strands 36, 37 twist equallyabout the common axis of symmetry 38, and a dashed line 392 indicates acutting plane along a cambered section 394 of the mesh bar 35. In thatFIG., an arrowed line 396 indicates a possible direction of a water flowvector past the mesh bar 35. A narrowest width of cork-screw-shaped meshbars 35 having the configuration illustrated in FIG. 28a at a bottom ofgrooves 391 measured parallel to the direction of the groove with aconventional vernier caliper approaches a diameter of the largestproduct strand 36 or 37 as the pitch increases, and a widest width atthe cambered section 394 is substantially equal to a sum of diameters ofthe product strands 36 and 37.

While for maximizing hydrodynamic lift and minimizing drag there existsan ideal orientation for the dashed line 392 indicating the camberedsection 394 with respect to the arrowed line 396 indicating the waterflow vector, the present invention permits engineering a trawl 13 havingnearly maximum lift while minimizing drag even though the angularrelationship between the dashed line 392 and the arrowed line 396varies. Thus, the arrowed line 396 may be parallel to the dashed line392, or may be skewed at an angle on either side of the dashed line 392as will likely occur due to flexing of the mesh cells 30 of the trawl 13during field operations in a water entrained environment. However, inassembling the trawl 13 or 263 the loose, corkscrew-shaped pitch of themesh bars 35 is engineered to properly orient the dashed line 392indicating the cambered section 394 with respect to the anticipatedorientation of arrowed line 396 indicating the water flow vectordepending upon the location of a mesh cell 30 or 280 within the trawl13, and upon the hydrodynamic characteristics of particular productstrands 36, 37 or straps 284 assembled into the mesh bars 35 or 283.

FIG. 28b depicts a configuration for the product strands 36, 37 in whichthe product strand 36 spirals around the product strand 37 which isaligned coaxially with the common axis of symmetry 38. Similar to theillustration of FIG. 28a, the dashed line 392 in FIG. 28b indicates thecutting plane through the mesh bar 35 along the cambered section 394 ofthe mesh bar 35, and the arrowed line 396 indicates a possible directionof the water flow vector past the mesh bar 35. Also similar to the meshbar 35 depicted in FIG. 28a, the narrowest width of corkscrew-shapedmesh bars 35 having the configuration illustrated in FIG. 28b at abottom of grooves 391 measured parallel to the direction of the groovewith a conventional vernier caliper approaches a diameter of the largestproduct strand 36 or 37, and the widest width at the cambered section394 is substantially equal to the sum of diameters of the productstrands 36 and 37. FIG. 28c depicts a configuration for product strands36, 37 in which a pair of product strands 37 spiral around the productstrand 36 which is aligned coaxially with the common axis of symmetry38. Similar to the illustration of FIGS. 28a and 28 b, a pair of dashedlines 392 in FIG. 28c indicate cutting planes through the mesh bar 35that pass through cambered sections 394, and a pair of arrowed lines 396indicate possible directions for the water flow vector past differentlocations along the mesh bar 35. In the forward section 24 of the trawl13, each mesh bar 35 made of product strands includes a series of atleast thirty-five (35) cambered sections 394. In the forward section ofthe trawl 263, each mesh bar 283 made of straps 284 includes a series ofat least twenty-five (25) cambered sections.

One characteristic of the mesh bar 35 depicted in FIG. 28 is that fieldoperations in a water entrained environment apply a force that urges theproduct strand 36 to slide along the product strand 37. FIG. 29 depictsa configuration for such a mesh bar 35 which prevents the product strand36 from sliding along the product strand 37 by including the productstrand 36 among strands 397 of a conventional braided sheath 398 thatencircles the product strand 37.

INDUSTRIAL APPLICABILITY

For many applications, various embodiments of the structures describedabove for the mesh bars 35 and 283 may be selected for assembly andarranged to form the trawl 13 or 263 so that hydrodynamic lift generatedby mesh bars 35 or 283 is directed substantially uniformly away from theaxis of symmetry 32 or 281 of the trawl 13 or 263. This configurationfor the mesh bars 35 or 283 yields maximum trawl volume. However, forother fishing conditions the orientation and design of the mesh bars 35or 283 may be arranged so cumulative lift created by the mesh bars 35 or283 of the bottom panel of the trawl 13 or 263, while directed away fromthe axis of symmetry 32 or 281 of the trawl 13 or 263, exhibits a lessermagnitude than cumulative lift created by the mesh bars 35 or 283 of thetop panel. In this latter configuration, the trawl 13 or 263 exhibits anet upward lift toward the surface 11 or 261 of the body of water 12 or262.

Although the present invention has been described in terms of thepresently preferred embodiments, it is to be understood that suchdisclosure is purely illustrative and is not to be interpreted aslimiting. Consequently, without departing from the spirit and scope ofthe invention, various alterations, modifications, and/or alternativeapplications of the invention will, no doubt, be suggested to thoseskilled in the art after having read the preceding disclosure.Accordingly, it is intended that the following claims be interpreted asencompassing all alterations, modifications, or alternative applicationsas fall within the true spirit and scope of the invention.

What is claimed is:
 1. A trawl which during field operations in a waterentrained environment becomes disposed about a central axis, the trawlcomprising: a plurality of mesh cells, each mesh cell including at leastthree mesh bars, during field operations of the trawl in a waterentrained environment at least a portion of at least one of said meshbars of at least one of the mesh cells generating hydrodynamic lift thataids in bettering a performance characteristic of a trawl system, theportion of mesh bars which generate hydrodynamic lift being.: a. offsetfrom the central axis of the trawl; b. formed by a strap assembled bylaminating together a plurality of rectangularly shaped straps andhaving a parallelogram cross-sectional shape so that movement of suchmesh bars through the water entrained environment relative to a waterflow vector creates a pressure differential across the portion of meshbars which generate hydrodynamic lift thereby establishing a lift vectorrelative to the central axis of the trawl, the water flow vector beingneither parallel nor perpendicular to the mesh bar; and c. each of themesh bars that generate hydrodynamic lift intersecting with at least oneother mesh bar; whereby the lift vector created by movement of the meshbars which have a portion that generates hydrodynamic lift through thewater entrained environment during field operations betters theperformance characteristic of the trawl which is selected from a groupconsisting of increased trawl volume, improved trawl shape, reducedvibration, reduced noise, and reduced drag.
 2. The trawl of claim 1wherein the portion of mesh bars which generate hydrodynamic lift areformed from bonded material.
 3. A trawl which during field operations ina water entrained environment becomes disposed about a central axis, thetrawl comprising: a plurality of mesh cells, each mesh cell including atleast three mesh bars, during field operations of the trawl in a waterentrained environment at least a portion of at least one of said meshbars of at least one of the mesh cells generating hydrodynamic lift thataids in bettering a performance characteristic of a trawl system, theportion of mesh bars which generate hydrodynamic lift being: a. offsetfrom the central axis of the trawl; b. formed with a hydrofoil shapethat: i. has a lay with a loose, corkscrew-shaped pitch establishing agroove; and ii. is oriented to establish leading and trailing edges forthe portion of mesh bars which generate hydrodynamic lift, both: (1) thelay of the portion of mesh bars which generate hydrodynamic lift havingan orientation relative to a receding direction; and (2) the leadingedge of the portion of mesh bars which generate hydrodynamic lift, whennormalized to the receding direction relative to said central axis,residing at a side of said mesh bars, the lay and residence of theleading edge being selected from a group consisting of:  (a) a left-handlay, and the leading edge being a right side of said mesh bar as viewedin the receding direction; and  (b) a right-hand lay, and the leadingedge being a left side of said mesh bar as viewed in the recedingdirection; so that movement of such mesh bars through the waterentrained environment relative to a water flow vector creates a pressuredifferential across the portion of mesh bars which generate hydrodynamiclift thereby establishing a lift vector relative to the central axis ofthe trawl, the water flow vector being neither parallel norperpendicular to the mesh bar; c. each of the mesh bars that generatehydrodynamic lift intersecting with at least one other mesh bar; and d.the portion of mesh bars which generate hydrodynamic lift being formedfrom a bonded material; whereby the lift vector created by movement ofthe mesh bars which have a portion that generates hydrodynamic liftthrough the water entrained environment during field operations bettersthe performance characteristic of the trawl which is selected from agroup consisting of increased trawl volume, improved trawl shape,reduced vibration, reduced noise, and reduced drag.
 4. A trawl whichduring field operations in a water entrained environment becomesdisposed about a central axis, the trawl comprising: a plurality of meshcells, each mesh cell including at least three mesh bars, a first and asecond of said mesh bars of at least one of the mesh cells being formedby straps and having at least one interconnecting connectiontherebetween fixed by laminating together short sections of strapsforming the first and the second of said mesh bars, during fieldoperations of the trawl in a water entrained environment at least aportion of both of the first and of the second of said mesh barsgenerating hydrodynamic lift that aids in bettering a performancecharacteristic of a trawl system, the portion of mesh bars whichgenerate hydrodynamic lift being: a. offset from the central axis of thetrawl; and b. formed with a hydrofoil shape that: i. has a lay with aloose, corkscrew-shaped pitch establishing a groove; and ii. is orientedto establish leading and trailing edges for the portion of mesh barswhich generate hydrodynamic lift, both: (1) the lay of the portion ofmesh bars which generate hydrodynamic lift having an orientationrelative to a receding direction; and (2) the leading edge of theportion of mesh bars which generate hydrodynamic lift, when normalizedto the receding direction relative to said central axis, residing at aside of said mesh bars, the lay and residence of the leading edge beingselected from a group consisting of: (a) a left-hand lay, and theleading edge being a right side of said mesh bar as viewed in thereceding direction; and (b) a right-hand lay, and the leading edge beinga left side of said mesh bar as viewed in the receding direction; sothat movement of such mesh bars through the water entrained environmentrelative to a water flow vector creates a pressure differential acrossthe portion of mesh bars which generate hydrodynamic lift therebyestablishing a lift vector relative to the central axis of the trawl,the water flow vector being neither parallel nor perpendicular to themesh bar; whereby the lift vector created by movement of the mesh barswhich have a portion that generates hydrodynamic lift through the waterentrained environment during field operations betters the performancecharacteristic of the trawl which is selected from a group consisting ofincreased trawl volume, improved trawl shape, reduced vibration, reducednoise, and reduced drag.
 5. The trawl of claim 4 wherein the portion ofmesh bars which generate hydrodynamic lift are formed from bondedmaterial.
 6. A trawl which during field operations in a water entrainedenvironment becomes disposed about a central axis, the trawl comprising:a plurality of mesh cells, each mesh cell including at least three meshbars, a first and a second of said mesh bars of at least one of the meshcells being formed by straps and having at least one flexibleinterconnecting connection therebetween which includes shackles that arejoined respectively to the first and second of said mesh bars and arealso mechanically joined together, during field operations of the trawlin a water entrained environment at least a portion of both of the firstand of the second of said mesh bars generating hydrodynamic lift thataids in bettering a performance characteristic of a trawl system, theportion of mesh bars which generate hydrodynamic lift being: a. offsetfrom the central axis of the trawl; and b. formed with a hydrofoil shapethat: i. has a lay with a loose, corkscrew-shaped pitch establishing agroove; and ii. is oriented to establish leading and trailing edges forthe portion of mesh bars which generate hydrodynamic lift, both: (1) thelay of the portion of mesh bars which generate hydrodynamic lift havingan orientation relative to a receding direction; and (2) the leadingedge of the portion of mesh bars which generate hydrodynamic lift, whennormalized to the receding direction relative to said central axis,residing at a side of said mesh bars, the lay and residence of theleading edge being selected from a group consisting of: (a) a left-handlay, and the leading edge being a right side of said mesh bar as viewedin the receding direction; and (b) a right-hand lay, and the leadingedge being a left side of said mesh bar as viewed in the recedingdirection; so that movement of such mesh bars through the waterentrained environment relative to a water flow vector creates a pressuredifferential across the portion of mesh bars which generate hydrodynamiclift thereby establishing a lift vector relative to the central axis ofthe trawl, the water flow vector being neither parallel norperpendicular to the mesh bar; whereby the lift vector created bymovement of the mesh bars which have a portion that generateshydrodynamic lift through the water entrained environment during fieldoperations betters the performance characteristic of the trawl which isselected from a group consisting of increased trawl volume, improvedtrawl shape, reduced vibration, reduced noise, and reduced drag.
 7. Thetrawl of claim 6 wherein the portion of mesh bars which generatehydrodynamic lift are formed from bonded material.